As a result of the tightly packed atoms and strong bonds of the diamond lattice, diamond is the best conductor of heat known at ambient temperatures. For instance, natural diamond conducts heat about five times better than copper at 300 Kelvin (K) with a conductivity about 2000 Watts per meter Kelvin (W/m K). Of the many uses of diamond where its high thermal conductivity plays a role, the use as a "heat sink", is probably the one which depends most directly on this property.
In electronic applications, the density of integrated circuits is limited by the large amount of heat generated by the extremely close packing of the electronic components on the chip, very high frequencies, and power density levels. To remove this heat, it is necessary to use hybrid circuits and bulky heat-dissipation devices or complicated and expensive refrigeration. New heat-sink materials are necessary.
Likewise, the production of laser diodes has led to extremely high intensity of light output, an output that is further augmented when the diodes are placed in arrays. Again, the limiting factor in the performance of the devices is the ability to dissipate the heat in the package.
The above problems can be solved by using diamond formed by chemical Vapor deposition, herein sometimes called CVD diamond. However, presently the thermal conductivity of CVD diamond differs from that of natural diamond in that it may vary through the thickness of a sample and is anisotropic. As discussed by M. Seal in the article, Thermal and Optical Applications of Thin Film Diamond, PHIL. TRANS R. SOC. LOND A (1993) pages 313-322, polycrystalline CVD diamond films show an anisotropy of thermal conductivity between directions parallel to (lateral) and perpendicular to the film plane. The thermal conductivity measured perpendicular to the plane was found to be at least 50% higher than that parallel to the plane. The conductivity has been found to vary inversely with the growth rate and Raman line width. Since the diamond layers are heat spreaders, it is the parallel or lateral conductivity which is limiting.
Thus, it would be desirable to provide a method to make synthetic diamond with high parallel and perpendicular thermal conductivity by CVD processes so that the overall conductivity is improved. It would also be desirable to produce CVD diamond with high thermal conductivity in shortened time periods.